A vulnerable species is a species of animals or plants which is likely to become endangered in near future. An endangered species is a species which is less in number and can be extinct in near future. Critically endangered species face an extremely high risk of extinction in the wild. Extinction is the end of an organism or of a group of organisms (taxon), normally a species. The moment of extinction is generally considered to be the death of the last individual of the species. Thus, the correct answer is option C.